2010年-世界发展银行全球_Climate_Change_Impacts_on_Agricultural_Yields_12页_551kb

Summary of "Climate Change Impacts on Agricultural Yields" (Background Note to the World Development Report 2010)

Core Content

This document analyzes the potential impacts of climate change on global agricultural yields, focusing on the period from 1996-2005 to 2046-2055. It uses the LPJmL model to simulate yield changes under different climate and CO₂ fertilization scenarios, considering the effects of temperature, precipitation, and CO₂ levels on crop productivity.

Main Points

• Model and Methodology:

  • The LPJmL model is used to simulate yield changes with a spatial resolution of 0.5° × 0.5°.
  • The model incorporates process-based implementations of gross primary production, growth and maintenance respiration, water-stress, and biomass allocation.
  • It dynamically computes the most suitable crop variety and growing period in each grid cell.
  • CO₂ fertilization effects and climate change are the primary drivers considered. Management intensity is calibrated to match FAOSTAT data for the 1990s.

• Scenarios and Data Sources:

  • 30 scenarios are computed from 1950 to 2055 using 3 emission scenarios (SRES A1b, A2, B1) and 5 GCMs.
  • Climate data are downscaled from monthly means of temperature and precipitation using bi-linear interpolation.
  • The number of wet days is kept constant after 2003 at the 30-year average of 1971-2000.

• Key Findings:

  • In 7 out of 10 world regions, crop yields are projected to increase from 1996-2005 to 2046-2055.
  • The overall impact on food self-sufficiency is negative in most regions due to population growth offsetting yield increases.
  • CO₂ fertilization has a significant effect on yield changes at the global and regional scale, but differences in climate projections have a larger influence at the national and sub-national levels.
  • There is considerable uncertainty in the future development of crop yields, ranging from a potential general decrease of 13% to an increase of 22% in 2050 relative to 2000.

Key Information

• Climate Change and CO₂ Fertilization:

  • CO₂ fertilization can enhance carbon assimilation and water-use efficiency, leading to potential yield increases.
  • However, the effectiveness of CO₂ fertilization is debated, and its benefits may not be fully realized due to nutrient limitations and changes in crop quality.

• Regional Impacts:

  • Northern high latitudes and mountainous regions are expected to see increased yields due to warming temperatures.
  • Tropical regions may experience yield decreases, especially when CO₂ fertilization effects are excluded.
  • MEA (Middle East and North Africa), AFR (Africa), LAM (Latin America), and EUR (Europe) show strong regional differences in yield projections due to varying climate patterns.

• Model Limitations:

  • The model accounts for adaptation in sowing dates but only for a few crops (wheat, maize, sunflower, and rapeseed).
  • Varieties for other crops are not adapted in the model, leading to potential underestimation of yield responses.
  • Simulations are simplified, and uncertainties remain due to the complexity of agricultural systems.

• Population and Food Security:

  • Population growth projections from Nakicenovic and Swart (2000) indicate that food self-sufficiency will likely decrease in most regions, even with increased yields.
  • Improved management, technological change, and expansion of agricultural land are necessary to meet future food demand.

Uncertainties and Challenges

• CO₂ Fertilization Uncertainty:

  • The potential benefits of CO₂ fertilization are not universally accepted and are subject to scientific debate.
  • Nutrient availability, especially nitrogen, is a critical factor in realizing these benefits.

• Climate Projections:

  • Differences in climate projections between GCMs are a major source of uncertainty in local and national yield assessments.
  • No single "most likely" climate change pattern can be identified.

• Adaptation and Management:

  • Farmers may adapt to climate change by selecting more suitable crop varieties and adjusting sowing dates.
  • However, the model does not fully account for these adaptations for all crops.

Conclusion

• Future crop yield projections are highly uncertain.
• CO₂ fertilization can have a positive impact on global and regional yields, but this is not guaranteed due to management constraints and other factors.
• Food self-sufficiency is expected to decrease in most regions due to population growth.
• Adaptation measures, improved management, and technological advancements are essential to address future food security challenges.

Figures and Tables

• Figure 2.2.1: Shows the mean change in crop yields across 30 scenarios for 1996-2005 to 2046-2055.
• Figure 2.2.2: Depicts the difference in yield changes with and without CO₂ fertilization.
• Figure 2.2.3: Highlights multi-scenario agreement on yield changes, with green areas indicating increases and red areas indicating decreases.
• Figure 2.2.4: Shows the standard deviation of yield changes across climate scenarios.
• Figure 2.2.5: Illustrates the impact of temperature rise on the shift from summer to winter wheat varieties.

Tables

• Table 2.2.1: Provides regional 5-GCM-mean yield changes with and without CO₂ fertilization.
• Table 2.2.2: Offers detailed regional percent crop yield changes in 2050 relative to 2000.
• Appendix Table: Maps countries to regions for the purpose of aggregating results.